Posted by vett on Tuesday, May 31, 2011 at 9:59pm.
We usually use Uppercase letters to represent angles, and lowercase for side lengths.
I resume the question as follows:
in abc, =60°,a=12, and b=5. find c.
We can solve this using the cosine rule:
c²=a²+b²-2abcos(C)
Substitute the numbers and take the square-root of c² to get c.
Use law of cosines:
c^2 = a^2 + b^2 - 2*a*b*cos(C)
c^2 = 12^2 + 5^2 - 2 * 12 * 5 * cos(60°)
c^2 = 144 + 25 - 120*cos(60°)
c^2 = 169 - 120 * 0.5
c^2 = 169 - 60 = 109
c = sqrt(109) = 10.4403
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